The present invention relates to the field of chemistry and ecology and more particularly to the remediation of environmental contaminants.
Contamination of the air, water and soil is a severe problem endangering the lives of many plants and animals, including humans. Many attempts have been made to reduce contamination by either preventing escape of the contaminants into the environment, containing the contaminants at one site, or treating the contaminants in some way to make them less harmful.
Halugenated Hydrocarbons
Halogenated hydrocarbons as a class of compounds are one of the most ubiquitous pollutants in the United States. Halogenated hydrocarbons have been and still are widely used in many industries as cleaning solvents, refrigerants, fumigants and starting materials for the syntheses of other chemicals. Because of the extensive use and stability of halogenated hydrocarbons, there are hundreds of contaminated groundwater and landfill sites in the United States, many of which are superfund sites for which there is no inexpensive, effective remediation technology available. Also, industrial waste treatment technology is expensive and not always effective. Among the individual organic chemicals, the most prevalent at superfund sites are trichloroethylene (TCE) and perchloroethylene (PCE). Because the natural attenuation of TCE and PCE appears to be slow, there is a great interest in finding ways to either accelerate degradation processes or use environmentally-friendly processes to remove the halocarbons.
Current methods for decontaminating ground water systems contaminated with halogenated hydrocarbon compounds or solvents involve pumping the water out of the reservoir and treating it with an "air stripping" treatment procedure. Halogenated hydrocarbons have also been remediated by a photolysis procedure wherein contaminated soil or sediment is placed on an oxide film and irradiated with concentrated sunlight to remove chloride atoms. These procedures are expensive and only successful if all of the contaminated material has been successfully removed from the site of contamination. Effective in situ treatment is not practiced because of a lack of treatment technology. Bioremediation has not been successful because maintenance of a viable microorganism population is not generally feasible in subsurface ecosystems. Chemical remediation processes have not been utilized because of the delivery of large amounts of the necessary chemicals and problems associated with groundwater hydrology.
Scientists have been studying the effects of metal powders or filings on halogenated hydrocarbon degradation kinetics. For example, Senzaki and Yasuo have reported the kinetics of the chemical reduction of organochloro compounds by treatment with iron powder. (Senzaki, T. and Yasuo, K., "Removal of organochloro compounds in water by reductive treatment: Reductive degradation of 1,1,2,2 tetrachloroethane with iron powder", Kogyo Yosiu, 357:2-7 (1988); Senzaki, T. and Yasuo, K., "Removal of Organic Chlorine Chemical Compounds by Use of Some Reduction Processes: Processing Trichloroethylene with iron powder", Kogyo Yosiu, 369:19-25 (1989)) More recently, Matheson and Tratnyek have reported the kinetics of the reaction of carbon tetrachloride and TCE with elemental iron (Matheson, L. J. and Tratnyek, P. G., "Reductive dehalogenation of chlorinated methanes by iron metal", Environ. Sci. Toxicol. 28:2045 (1994)) and Gillham has reported removal of 90% of TCE and 88% of PCE from aquifer groundwater by passage through a 1.5 m thick permeable reactive wall consisting of 22 wt % granular iron and 78 wt % sand. (Gillham, R.W., Book of Abstracts, 209th ACS National Meeting, Vol. 35:691-693, Apr. 2-7, 1995.) However, the observed kinetics of these reactions are slow, and the reactions often result in insufficient or incomplete degradation. Others have tried to find ways to enhance the speed of the reaction using catalysts or anaerobic conditions. For example, U.S. Pat. No. 4,382,865 to Sweeny discusses degradation of certain reducible organic compounds in waste water streams by passing the stream through a column or reservoir containing copper-catalyzed iron, and U.S. Pat. No. 5,266,213 to Gillham discusses the remediation of groundwater contaminated with halogenated organic compounds in which the water is passed through a trench or into an enclosed tank containing iron filings under strictly anaerobic conditions. However, these methods fail to provide degradation of halogenated hydrocarbons in soils and sediments and fail to provide complete degradation of halogenated hydrocarbons in aquifers in a rapid, efficient and inexpensive manner.
Pesticides
A large number of pesticide-contaminated sites exist throughout the world, posing both human and ecological risks. These sites include contaminated soils, sediments and natural waters that have occurred as a result of industrial spills, agricultural applications, and environmental transport phenomena. Many of the pesticides contaminating these sites are known to be extremely toxic and persistent in the environment. Therefore, technology is needed to remediate these contaminated sites.
Some of the most environmentally persistent pesticides are the chlorinated aliphatics such as toxaphene, DDT, chordane, lindane, heptachlor, endrin, dieldrin, aldrin, and methoxychlor. Many superfund sites throughout the United States have been identified as contaminated with these and similar pesticides. No rapid environmental transformation pathways exist for many of these compounds, resulting in a lack of natural attenuation. For example, toxaphene is so long-lived in the environment that it has been suggested that it could outlive mankind.
Classes of pesticides that are somewhat less persistent still pose pollution problems in sediments, soils, and natural waters, and require remediation technology to clean up the sites. For example, the organophosphates organophosphorothioates and organophosphoro-dithrionates, while not as persistent as the halogenated hydrocarbons, are more widely used and contaminate many sites. These classes of pesticides include methyl parathion, chloropyriphos, fenthion and malathion. Also included within these classes of less persistent compounds are many chemical warfare agents such as the nerve gases.
Some attempts have been made to provide methods for the remediation of pesticides using metals. For example, U.S. Pat. No. 3,640,821 to Sweeny et al. discusses reductive degradation of the pesticide DDT by reacting the DDT with finely divided zinc at a pH less than 4, and U.S. Pat. No. 3,737,384 to Sweeny et al. discusses decomposition of DDT by reaction with a metal, such as iron, coated with a thin layer of a catalytic metal such as copper or silver under mildly acidic conditions. However, these methods are inefficient, time-consuming and expensive, and the metals are often toxic.
Dye and Dye Wastes
Dye manufacturing and fiber dying processes generate large quantities of dye wastes in the United States. Many of these dyes, dye mixtures, and other components of dye waste are large molecular weight compounds that are poorly degraded by biotic processes in waste water treatment systems or in the receiving waters. Also, the releasing of dye wastes in environmental receiving waters is partially regulated based on the color of the waste water effluent. U.S. Pat. No. 4,194,973 to Smith describes treatment of certain dyes with Fe(II) in the presence of iron. However elevated temperatures are required for efficient remediation, and the products produced by these reactions are not known. Thus, methodology is needed that will inexpensively decompose these large dye molecules into lower molecular weight compounds with concurrent loss of color so that biotic processes may prevail. One area in which this need exists is in those industries discharging waste waters containing chromophoric compounds such as aryl azo- or aryl nitro-containing compounds. In particular, remediation of dyes such as Direct Blue 75, Disperse Blue 79, Acid Red 4 (Acid Eosine G), Acid Blue 40, Direct Yellow 137, Direct Red 24, and Acid Yellow 151 is needed.
It would be of great environmental benefit to have an inexpensive method of degrading contaminants such as halogenated hydrocarbons, pesticides, and dyes in soils, waters, sediments, and aquifer materials that results in products that are environmentally acceptable.